INCOME TAXES - Significant Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax asset:
Net operating loss carry forwards		$ 3,405
Capitalized technology license	$ 804	4,163
Capitalized research expenditures	3,719	8,100
Accruals and reserves	962	6,712
Retirement plan	7,125	9,723
Deferred revenue	206	516
Tax credit carry forwards	21,562	1,846
Stock-based compensation	1,819	2,889
Other	59	874
Deferred Tax Assets, Gross	36,256	38,228
Valuation allowance	(2,460)	(7,950)
Deferred tax assets	33,796	30,278
Deferred tax liability:
Accruals and reserves	(6,774)	(5,785)
Deferred tax liabilities	(6,774)	(5,785)
Net deferred tax assets	$ 27,022	$ 24,493